Heathkit SB-230 Amp

You dont run those tetrodes in GG and you need a screen and bias supply. Its a good candidate for a medical pull 3CPX800A7 ($200-300)and a little bit of air and a filament xfmr.

Carl

 

This is very true....

 

Negative. It's a good candidate for leaving it as close to original as possible, and selling it for megabux like this one. $545 will go a long way to buying parts to build an amplifier the way you want. BTW, that SB-230 got 19 bids from 6 bidders (five bidders are still looking).

 

Tonight I completed the diode board and it works great! Tommorrow I will post the pix of the diode board manufacture and install. But it didn't go easy! Once again, a Design error messed with me but luckily didn't blow anything up

 

Not if you use a SMPS like W5JGV has done (http://w5jgv.com/hv-ps1/) using NO heavy and expensive iron. HV is regulated, too.

There are LOTS better options than 572Bs. Various ceramic triodes are good WAY past 6m.

 

The SB-230 was fired up yesterday evening after the diode board was made. It turns out I reversed the diode string, so I had to pull half of them out and mount them the other direction. That was because I used 6 1N5408s instead of the 7 Heathkit type diodes. But all is well and it powered up nicely with full voltage. Probably down abit, so I should probably replace the three 1M resistors in the meter string. Today, after the church picnic, I need to build up the soft key circuit. I might build a soft start too, like I did for the SB-200. All these mods only enhance the amps value. I have already verified the tube puts out 500W, so it is good to go. But, I STILL need a power transformer to build another amp, so I am right back to square 1. Guess this SB-230 will go into Museum service. I notice the front panel has alot of smoke residue on it. Hafta clean that off. Also need to improvise a meter backlight. Heathkit used an obscure 28V lamp for some silly reason. I might try some LED backlighting.

 

Good to hear everything is working fine.

 

Thats fine for a driver stage; or an AM modulator PS if its clean enough. When there is a reliable and relatively inexpensive switcher that will supply 2500-4000V at enough VA for a minimum of 2000W CCS of RF I'll get interested.

Carl

 

Since each resistor has close to 1KV across it, be sure to use resistors rated for the voltage. Heathkit used 2W resistors but, each resistor needs to dissipate only approximately 670mW. I used Vishay VR68 series resistors in my SB-220.

The backlight is in series with two 500/5W resistors, across one of the transformer primaries. That's why they used a 28V lamp. They're not hard to find. LEDs tend to have a "spotlight" effect, even if you use types with a wider dispersion angle and/or scuff the lens with sandpaper. Buy a new lamp when you buy HV meter resistors.

There are lots of transformer options, if you look. It doesn't have to cost a lot. The free xfmr I rewound set me back only about $100 for materials. It's good for up to 4000VDC @ 1.5A. The SMPS topology looks interesting. Like anything, it can be scaled to suit.

That was only ONE example, to show it can be done on a small scale. SMPS have been around for decades. Going back to the 70s, I've seen them supply several clean KVA.

 

Switchers have always been noisy and unreliable at producing amp level HV unless severe overkill is employed. The few who have published in ham journals and attempted to commercialize it are mere footnotes. By the time a HV switcher can compete with a legal limit + overhead linear mode PS in all aspects, will be around the time SS becomes the majority choice, and its certainly not a market Id want to invest in.

While Im very aware of Ralphs excellent reputation and other projects its not something Id spend hobby time building but it might appeal to a few others with a dead Heath Warrior or other 4 x 811A amp. If it was my amp Id buy the AL-811 transformer for $105 and a handfull of caps and be done with it. Last year when that transformer was $89 I resurrected an early Dentron 160-10L for a customer.

Carl